1. Field of the Invention
The present invention relates to adhesive compositions for bonding metal to rubber. More particularly, the present invention relates to water-based adhesives for bonding metals to vulcanizable rubbers; to methods for making such adhesives; to methods for bonding metals to vulcanizable rubbers using such adhesives; and to the bonded articles produced thereby.
2. Background of the Invention and Relevant Materials
Adhesives used in the bonding of natural and synthetic rubbers to substrates, including metal substrates, commonly employ a solvent base and are generally activated by the vulcanization process. This is, at least in part, because volatile solvents such as toluene and xylene exhibit a high level of compatibility with the classes of compounds that provide the ingredients for such adhesives, and also tend to wet out the substrates effectively.
While solvent-based adhesives generally provide good adhesion, they also possess many undesirable qualities from the viewpoint of health, safety, and environmental quality. The solvents are usually toxic, presenting a health risk to those who come into contact with the solvents; with the adhesives containing the solvents; or with the fumes generated by either.
In addition, the volatility of both the solvents and their fumes presents the risk of fire or explosion during manufacture, packaging, shipping, and use of solvent-based adhesives.
Environmental concerns, especially as reflected in and enforced through state and federal laws and regulations, further detract from the desirability of using solvent-based adhesives.
These problems can be avoided through the use of water-based adhesives, such as those described in SADOWSKI, U.S. Pat. No. 4,483,962. SADOWSKI discloses aqueous adhesive systems which employ a terpolymer latex formed by the emulsion polymerization of 2,3-dichloro-1,3-butadiene and a mixture of at least two different unsaturated monomers copolymerizable therewith.
Unfortunately, while water-based adhesives do not suffer from the health, safety, and environmental impact problems of solvent-based adhesives, they do exhibit performance drawbacks that have significantly limited their range of application. These drawbacks, and particularly lack of adequate holding power, are most evident under conditions of environmental stress, and especially under conditions of heat, moisture, or a combination of both.
Therefore, in high stress applications the benign qualities of water-based adhesives have been outweighed by the need for dependable performance, which has instead dictated the use of solvent-based adhesives notwithstanding their associated problems.